Listing account calendars on the shell, some visual state updates and reacting to calendar setting changes properly.

Wino.Calendar.ViewModels/Data/GroupedAccountCalendarViewModel.cs

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+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.Collections.Specialized;
+using System.Linq;
+using CommunityToolkit.Mvvm.ComponentModel;
+using Wino.Core.Domain.Entities.Shared;
+
+namespace Wino.Calendar.ViewModels.Data
+{
+    public partial class GroupedAccountCalendarViewModel : ObservableObject
+    {
+        public MailAccount Account { get; }
+        public ObservableCollection<AccountCalendarViewModel> AccountCalendars { get; }
+
+        public GroupedAccountCalendarViewModel(MailAccount account, IEnumerable<AccountCalendarViewModel> calendarViewModels)
+        {
+            Account = account;
+            AccountCalendars = new ObservableCollection<AccountCalendarViewModel>(calendarViewModels);
+
+            ManageIsCheckedState();
+
+            foreach (var calendarViewModel in calendarViewModels)
+            {
+                calendarViewModel.PropertyChanged += CalendarPropertyChanged;
+            }
+
+            AccountCalendars.CollectionChanged += CalendarListUpdated;
+        }
+
+        private void CalendarListUpdated(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
+        {
+            if (e.Action == NotifyCollectionChangedAction.Add)
+            {
+                foreach (AccountCalendarViewModel calendar in e.NewItems)
+                {
+                    calendar.PropertyChanged += CalendarPropertyChanged;
+                }
+            }
+            else if (e.Action == NotifyCollectionChangedAction.Remove)
+            {
+                foreach (AccountCalendarViewModel calendar in e.OldItems)
+                {
+                    calendar.PropertyChanged -= CalendarPropertyChanged;
+                }
+            }
+            else if (e.Action == NotifyCollectionChangedAction.Reset)
+            {
+                foreach (AccountCalendarViewModel calendar in e.OldItems)
+                {
+                    calendar.PropertyChanged -= CalendarPropertyChanged;
+                }
+            }
+        }
+
+        private void CalendarPropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
+        {
+            if (sender is AccountCalendarViewModel viewModel)
+            {
+                if (e.PropertyName == nameof(AccountCalendarViewModel.IsChecked))
+                {
+                    ManageIsCheckedState();
+                }
+            }
+        }
+
+        [ObservableProperty]
+        private bool _isExpanded = true;
+
+        [ObservableProperty]
+        private bool? isCheckedState = true;
+
+        private bool _isExternalPropChangeBlocked = false;
+
+        private void ManageIsCheckedState()
+        {
+            _isExternalPropChangeBlocked = true;
+
+            if (AccountCalendars.All(c => c.IsChecked))
+            {
+                IsCheckedState = true;
+            }
+            else if (AccountCalendars.All(c => !c.IsChecked))
+            {
+                IsCheckedState = false;
+            }
+            else
+            {
+                IsCheckedState = null;
+            }
+
+            _isExternalPropChangeBlocked = false;
+        }
+
+        partial void OnIsCheckedStateChanged(bool? newValue)
+        {
+            if (_isExternalPropChangeBlocked) return;
+
+            if (newValue == null)
+            {
+                // Only primary calendars must be checked.
+
+                foreach (var calendar in AccountCalendars)
+                {
+                    calendar.IsChecked = calendar.IsPrimary;
+                }
+            }
+            else
+            {
+                foreach (var calendar in AccountCalendars)
+                {
+                    calendar.IsChecked = newValue.GetValueOrDefault();
+                }
+            }
+        }
+    }
+}